Forming a non-planar transistor having a quantum well channel

ABSTRACT

In one embodiment, the present invention includes an apparatus having a substrate, a buried oxide layer formed on the substrate, a silicon on insulator (SOI) core formed on the buried oxide layer, a compressive strained quantum well (QW) layer wrapped around the SOI core, and a tensile strained silicon layer wrapped around the QW layer. Other embodiments are described and claimed.

This application is a continuation of U.S. patent application Ser. No.11/728,891, filed Mar. 27, 2007 now U.S. Pat. No. 7,928,426, the contentof which is hereby incorporated by reference.

BACKGROUND

A variety of electronic and optoelectronic devices can be enabled bydeveloping thin film relaxed lattice constant III-V semiconductors onelemental silicon (Si) substrates. Surface layers capable of achievingthe performance advantages of III-V materials may host a variety of highperformance electronic devices such as complementary metal oxidesemiconductor (CMOS) and quantum well (QW) transistors fabricated fromextreme high mobility materials such as, but not limited to, indiumantimonide (InSb), indium gallium arsenide (InGaAs) and indium arsenide(InAs). While such high mobility QW channels have been incorporated intoplanar transistors, they have not been incorporated into non-planartransistors.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross section view of a device structure in accordance withan embodiment of the present invention.

FIG. 2 is a band diagram of a structure in accordance with an embodimentof the present invention.

FIG. 3 is a flow diagram of a method in accordance with an embodiment ofthe present invention.

DETAILED DESCRIPTION

In various embodiments, a high-mobility strained quantum well (QW)channel may be incorporated into a non-planar structure such as anon-planar metal oxide semiconductor field effect transistor (MOSFET).Such non-planar transistors include a silicon structure or fin formed onan underlying-oxide layer, and in turn a gate structure can be formedaround the silicon fin. In this way, high mobility channels withexcellent electrostatic control can be achieved for ultimate channellength scalability. Furthermore, tensile and compressive strain may besimultaneously introduced to respectively optimize electron transport insilicon for n-channel MOSFETs (NMOS) and hole transport in germanium(Ge) for p-channel MOSFETs (PMOS) using a common material core.Furthermore, correct and sufficient conduction and valence band offsetsprovide for electron and hole confinement. Using embodiments, transistordevices may be formed using conventional stack engineering, as anoutermost core layer may be formed of silicon to allow formation of agate stack thereon.

Referring now to FIG. 1, shown is a cross section view of a devicestructure 10 in accordance with an embodiment of the present invention.As shown in FIG. 1, structure 10 may be used to form NMOS or PMOSdevices on a substrate 30. In various embodiments, substrate 30 may be ahigh resistivity n or p-type (100) off-oriented Si substrate, althoughthe scope of the present invention is not limited in this regard. Asshown in FIG. 1, next a buried oxide layer 34 may be formed on substrate30. In various embodiments, buried oxide layer 34 may be formed of asuitable oxide material such as silicon dioxide (SiO₂) or other oxide.

Still referring to FIG. 1, next a silicon on insulator (SOI) layer maybe formed. Specifically, a SOI layer may be deposited (or bonded) andpatterned to obtain a SOI core 40, which is a non-planar structure onburied oxide layer 34. Note this SOI core is formed of a silicon fin ornarrow strip that has a width much less than the extent of buried oxidelayer 34. Note, this layer may also be strained. As shown in FIG. 1, acompressive strained QW layer 42 may be wrapped around SOI core 40. Invarious embodiments, QW layer 42 may be a Ge layer selectively grown onSOI core 40. The growth may be conducted by vapor deposition method andthickness can range from 1 nanometers (nm)-20 nm. Next, a tensilestrained Si layer 44 may be formed on QW layer 42. In variousembodiments, Si layer 44 may be selectively grown to wrap around QWlayer 42. The growth may be conducted by vapor deposition method andthickness can range from 1 nm-20 nm. Using this configuration, holes(electrons) may travel and be confined within QW layer 42 for highmobility conduction.

Referring still to FIG. 1, next a gate dielectric layer 46 may be formedover Si layer 44. In various embodiments, a conformal gate dielectriclayer may be formed using an atomic layer deposition (ALD) to thus wraparound the core formed of Si/Ge/SOI. In various embodiments, gatedielectric layer 46 may be formed using a low dielectric constant(low-k) material such as a carbon doped oxide or other such dielectric.Over gate dielectric layer 46, a gate electrode layer 48 may be formed.In various embodiments, an ALD process may be used to form conformalgate electrode layer 48. Note that in various embodiments, similar ordifferent electrode materials may be used for n-channel and p-channelMOSFETs.

While shown with this particular implementation in the embodiment ofFIG. 1, the scope of the present invention is not limited in thisregard. For example, in other embodiments a bulk Si substrate may beused with appropriate isolation to form the Si core (i.e., over a givenSOI substrate). Furthermore, instead of a QW layer formed of pure Ge, aQW layer may be formed using high Ge content silicon germanium (SiGe)with compressive strain. In various embodiments, the Ge concentrationmay be between approximately 10% and 100%. In this way, thicker QWs maybe realized for particular applications. While not shown in FIG. 1, afully completed device may further include source and drain electrodesformed of a contact layer. For an NMOS device, the contact layer may ben+doped, while for a PMOS device, the contact layer may be p+doped.

Accordingly, in various embodiments non-planar transistor devices may beformed using a high mobility material to form high electron mobilitytransistors (HEMTs) or high hole mobility transistors (HHMTs) or highhole mobility transistors (HHMTs) having high speed and low powerconsumption. Such devices may have dimensions less than approximately 50nm with a switching frequency of approximately 562 gigahertz (GHz). Suchdevices may be able to operate at between approximately 0.5-1.0 voltswithout significant reduction of drive current. Furthermore, embodimentsmay provide lower gate delay at a gate length than a silicon baseddevice.

Referring now to FIG. 2, shown is a band diagram of a structure inaccordance with an embodiment of the present invention. As shown in FIG.2, the band diagram illustrates, via the top line a conduction band(i.e., E_(C)) and via the lower line a valence band (i.e., E_(V)).Beginning at the left-hand side of FIG. 2, the SOI layer, which may bepure silicon, is formed. Over this layer, a QW layer, which may beformed of compressive strain germanium or silicon germanium (SiGe) maybe formed. The QW channel layer may be formed having a smaller bandgapthan the SOI core. Over the QW channel layer, an upper tensile strainedsilicon layer may be formed that may, in some embodiments have a smallerbandgap than the SOI core, but a layer bandgap than the QW channellayer. Then, as shown in FIG. 2, a dielectric layer may be formed overthe silicon layer which has a larger bandgap than the other layers. Asshown in FIG. 2, the Ge layer provides a QW for holes and the Si layerprovides the QW for electrons.

Referring now to FIG. 3, shown is a flow diagram of a method inaccordance with an embodiment of the present invention. As shown in FIG.3, method 100 may begin by forming a buried oxide layer over a Sisubstrate (block 110). Next, a SOI core may be formed over the buriedoxide layer (block 120). For example, a silicon layer may be deposited(or bonded) and patterned to form the SOI core. Then a QW layer may bewrapped around the SOI core (block 130). For example, in one embodimenta strained compressive Ge or SiGe layer may be grown on the SOI core.Above the QW layer, an Si layer may be formed to wrap around the QWlayer (block 140). Then a gate stack may be formed over the structure,including a dielectric layer and a gate electrode (block 150). Invarious embodiments, ALD processes may be performed to obtain aconformal gate dielectric layer and a conformal gate electrode. In thisway, a non-planar transistor having high mobility may be formed.

While the present invention has been described with respect to a limitednumber of embodiments, those skilled in the art will appreciate numerousmodifications and variations therefrom. It is intended that the appendedclaims cover all such modifications and variations as fall within thetrue spirit and scope of this present invention.

1. An apparatus comprising: a substrate; a buried oxide layer directlyformed on the substrate; a silicon on insulator (SOI) core formeddirectly on the buried oxide layer, the SOI core formed of a silicon finon the buried oxide layer; a quantum well (QW) layer wrapped directlyaround the SOI core, wherein the QW layer is formed of silicon germanium(SiGe) having a Ge concentration of at least approximately 10%; and asilicon layer wrapped around the QW layer.
 2. The apparatus of claim 1,further comprising: a gate dielectric layer formed over the siliconlayer; and a gate electrode layer formed over the gate dielectric layer.3. The apparatus of claim 1, wherein the apparatus comprises anon-planar transistor, wherein the quantum well layer comprises achannel of the non-planar transistor.
 4. The apparatus of claim 3,wherein the non-planar transistor comprises a high electron mobilitytransistor (HEMT) or a high hole mobility transistor (HHMT).
 5. Theapparatus of claim 1, wherein the silicon layer has a smaller bandgapthan the SOI core and a larger bandgap than the QW layer.
 6. Theapparatus of claim 1, wherein the QW layer is compressive strained. 7.The apparatus of claim 6, wherein the silicon layer is tensile strained.8. An apparatus comprising: a high electron mobility transistor (HEMT)including: a substrate; a buried oxide layer directly formed on thesubstrate; a silicon on insulator (SOI) core formed directly on theburied oxide layer, the SOI core formed of a silicon fin on the buriedoxide layer; a quantum well (QW) layer wrapped directly around the SOIcore, wherein the QW layer is formed of silicon germanium (SiGe) havinga Ge concentration of at least approximately 10%; and a silicon layerwrapped around the QW layer, wherein the silicon layer has a smallerbandgap than the SOI core and a larger bandgap than the QW layer.
 9. Theapparatus of claim 8, further comprising: a gate dielectric layer formedover the silicon layer; and a gate electrode layer formed over the gatedielectric layer.
 10. The apparatus of claim 9, wherein the siliconlayer is tensile strained.
 11. The apparatus of claim 10, wherein the QWlayer is compressive strained.
 12. The apparatus of claim 11, whereinthe compressive strain and the tensile strain is to optimize transportof electrons and holes.